CN110792519A

CN110792519A - Method for starting an internal combustion engine

Info

Publication number: CN110792519A
Application number: CN201910717462.8A
Authority: CN
Inventors: C.克拉特; J.朗格; M.昂特基尔舍; U.班尼克
Original assignee: Andreas Stihl AG and Co KG
Current assignee: Andreas Stihl AG and Co KG
Priority date: 2018-08-03
Filing date: 2019-08-05
Publication date: 2020-02-14
Anticipated expiration: 2039-08-05
Also published as: EP3604778B1; CN110792519B; EP3604778A1; US10774804B2; US20200040863A1

Abstract

The invention relates to a method for safely starting an internal combustion engine (3) in a handheld portable work apparatus (1). At the time of start, when the rotational speed (n) of the internal combustion engine (3) exceeds an activation rotational speed (ADZ) above an engagement rotational speed (EKD) of the centrifugal force clutch (7), a start rotational speed limiting mechanism (12) is activated. After the activation of the start-up speed limiting means (12), the ignition means (11) is intervened in at least one operating cycle (ASP) of the internal combustion engine (3) in such a way that the speed (n) of the internal combustion engine (3) is reduced. After the rotational speed (n) has dropped below the lower intervention rotational speed (47), the ignition device (11) is intervened in such a way that the rotational speed (n) increases. When the speed (n) exceeds the upper intervention speed (49), the ignition device (11) is again intervened in such a way that the speed (n) drops. As the number of successive work cycles (ASP) increases, the upper intervention speed (49) and/or the lower intervention speed (47) changes.

Description

Method for starting an internal combustion engine

Technical Field

The invention relates to a method for starting an internal combustion engine in a handheld portable work apparatus, wherein a tool of the work apparatus is drivingly connected to a crankshaft of the internal combustion engine via a centrifugal force clutch. The centrifugal force clutch drives the tool when the rotational speed of the internal combustion engine exceeds the engagement rotational speed of the centrifugal force clutch. In order to control the rotational speed of the internal combustion engine, a control unit is provided which intervenes in the ignition as a function of the determined rotational speed of the internal combustion engine.

Background

In many hand-held portable work implements, the internal combustion engine is manually started, for example, by a pull-cord starter. At the start, it is advantageous if the centrifugal clutch is not closed in an uncontrolled manner, so that the tool is separated from the driving crankshaft of the internal combustion engine during the starting process.

Furthermore, undesirable operating conditions of the internal combustion engine may occur, for example, as a result of a malfunction at the mixture forming device, which may lead to an excessively high rotational speed of the internal combustion engine at start-up.

Disclosure of Invention

The object of the present invention is to provide a method for starting an internal combustion engine, by means of which undesired operating conditions of the internal combustion engine are detected in order to ensure a reliable start of the internal combustion engine.

This object is achieved in that, at the start, the start rotational speed limiting means becomes active and intervenes in the ignition means of the internal combustion engine when the rotational speed of the internal combustion engine exceeds an activation rotational speed that is above the engagement rotational speed of the centrifugal force clutch.

If the rotational speed does not rise above the activation rotational speed during the start-up and initial operation of the internal combustion engine, the start-up rotational speed limiting means remains switched off or in the "standby" mode, in which the start-up rotational speed limiting means does not interfere with the operation of the internal combustion engine. The activation speed limiting mechanism remains inactive.

If the activation speed is exceeded, the start speed limiting means intervenes in the ignition means for at least one operating cycle of the internal combustion engine in such a way that the speed of the internal combustion engine is reduced. After the rotational speed of the internal combustion engine has dropped below the lower intervention rotational speed, the ignition is again intervened in such a way that the rotational speed of the internal combustion engine is increased again. The lower intervention speed is below the upper intervention speed at a speed interval (Drehzahlabstand). The upper intervention speed may preferably be equal to or less than the activation speed. As soon as the rising rotational speed of the internal combustion engine exceeds the upper intervening rotational speed, the ignition device is again affected by the start rotational speed limiting device in such a way that the rotational speed drops again. The start speed limiting device can set the speed of the internal combustion engine in a speed path (Drehzahlkorridor) between the upper intervention speed and the lower dry run-in speed. In this case, it is advantageously provided that the upper intervention speed and/or the lower preliminary speed is changed as the number of successive operating cycles increases.

The upper intervention speed is the limit speed. The upper intervention speed may also be referred to as an upper speed threshold, above which the ignition mechanism is changed to reduce the speed. The dry pre-rotation speed is accordingly the limit rotation speed. The dry pre-rotation speed may also be referred to as a lower rotation speed threshold below which the ignition mechanism is changed to increase the rotation speed.

With the method according to the invention, the internal combustion engine can be started reliably while avoiding undesirable operating conditions.

After the internal combustion engine has started running, the upper intervention speed and/or the dry pre-rotation speed are advantageously reduced. The upper intervention speed is in particular reduced below the engagement speed. This ensures that the rotational speed of the internal combustion engine is brought below the engagement rotational speed after the internal combustion engine is started and after the internal combustion engine starts to operate. After the upper intervention speed has dropped, the internal combustion engine is ensured to be operated at a safe speed interval below the engagement speed.

The change of the ignition mechanism can be done by adjusting the ignition time point. The change of the ignition mechanism is advantageously accomplished by switching the ignition mechanism off and on.

In a further development of the invention, the upper intervention speed can be a clock output speed, which advantageously forms the upper speed threshold. As the clock output speed is exceeded, the ignition mechanism is switched off.

The lower intervention speed may advantageously be a clock input speed, which advantageously forms the lower speed threshold. With the clock input threshold being undershot, the ignition mechanism is turned on.

The upper intervention speed is advantageously plotted as a characteristic curve for a continuous operating cycle. In the same way, the lower intervention speed can be configured as a characteristic curve for a continuous operating cycle.

The characteristic curve is not only a stored characteristic curve, but also a characteristic curve field stored in a memory and/or a characteristic curve predefined or generated by an algorithm. It can thus be checked by inputting, for example, the determined rotational speed into a predefined algorithm, depending on variables such as the counted number of operating cycles after the internal combustion engine has started and started running, whether the limit rotational speed is exceeded or not exceeded, as described above, as an intervention rotational speed and/or a dry predicted rotational speed.

After a successful start and start of operation of the internal combustion engine, the characteristic curves of the upper and lower intervention speeds extend at least partially parallel to one another, in particular as far as possible, after a predetermined number of operating cycles. Advantageously, the characteristic curve of the upper intervention speed and/or of the dry pre-rotation speed is changed by the number of successive operating cycles. The characteristic curves of the upper and lower intervention speeds are expediently reduced by the same amount. The characteristic curves are preferably changed jointly. It may be advantageous if the characteristic curves of the upper and lower intervention speeds are reduced by different values. In particular, after a predetermined number of operating cycles, the upper intervention rotational speed is below the engagement rotational speed of the centrifugal force clutch at a safe rotational speed interval.

In particular, the activation rotational speed of the characteristic curve, which can be configured to be plotted over successive operating cycles, can be equal to or greater than the upper intervention rotational speed. The characteristic curve is preferably constant and extends in particular horizontally to the X axis. The activation rotational speed preferably forms an unchangeable activation threshold. The activation rotational speed is preferably not changed during the operation of the method. The activation rotational speed is a fixed rotational speed value. It may be expedient to set an activation rotational speed that can be varied in relation to the working cycle. The activation rotational speed is advantageously not below the upper intervention rotational speed.

In one embodiment of the invention, the upper intervention speed may be allowed to be exceeded after the start of the internal combustion engine after the end of the first time window if a condition is fulfilled that the speed of the internal combustion engine is below the upper intervention speed for the entire duration of the first time window. The first time window is preferably started with a first crankshaft rotation at the start of the internal combustion engine, in particular with a first crankshaft rotation. A first time window is initiated upon application of a first voltage of a generator driven by the crankshaft. When a single or several operating parameters are fulfilled for switching off the starting rotational speed limiting means, it may be advantageous to switch off the starting rotational speed limiting means, for example depending on an operating change signal of the internal combustion engine or on an ignition control of the internal combustion engine, as described in the applicant's patent application DE 102011010069 a1, the disclosure of which is hereby incorporated by reference.

If the rotational speed of the internal combustion engine exceeds the activation rotational speed, in particular during the duration of the first time window, the second time window is started. If the rotational speed of the internal combustion engine is not safely below the upper intervention rotational speed for the duration of the third time window, the internal combustion engine is switched off.

In order to coordinate the method, it is expedient if the duration of the second time window is advantageously longer than the duration of the first time window and/or the duration of the third time window. The duration of the second time window is in particular at least a multiple longer than the duration of the third time window. The duration of the first time window is in particular longer than the duration of the third time window.

In the operation of the start-up speed limiting device, the third time window is restarted with each undershooting of the dry pre-ignition speed and with the intervention of the ignition device. If the ignition is not again intervened to reduce the rotational speed during the duration of the third time window, an exceeding of the upper intervening rotational speed may be permitted.

The method according to the invention is particularly advantageous in internal combustion engines to be started by a pull-cord starter.

Drawings

Further features of the invention emerge from the further claims, the description and the drawing, in which an embodiment of the method according to the invention is described below. In the drawings:

fig. 1 shows a schematic representation of a handheld portable work apparatus, for example a free cutting machine (Freischneiders);

fig. 2 depicts a diagram of the characteristic curves of the activation rotational speed, the clock output rotational speed (Austaktdrehzahl) as the upper intervention rotational speed and the clock input rotational speed (einkaktdrehzahl) as the lower intervention rotational speed for a continuous (aftermathoil) duty cycle (Arbeitsspiele) after the internal combustion engine has been started and started;

fig. 3 is a schematic flow diagram of a method for starting an internal combustion engine in a handheld portable work apparatus according to the invention;

FIG. 4 is a schematic illustration of an allowed rotational speed curve between a clock output rotational speed as an upper intervening rotational speed and a clock input rotational speed as a lower intervening rotational speed when starting the internal combustion engine;

FIG. 5 is a schematic illustration similar to FIG. 4 of a speed curve between a clock output speed as an upper intervention speed and a clock input speed as a lower intervention speed, with repeated overshooting and undershooting of the clock output speed;

fig. 6 is a schematic illustration of a speed curve similar to fig. 5 between a clock output speed as an upper intervention speed and a clock input speed as a lower intervention speed, with a clock output speed which is rarely exceeded and a clock input speed which is less undershot.

Detailed Description

The work implement shown schematically in fig. 1 has a housing 2 with an internal combustion engine 3 arranged therein. The work implement 1 shown by way of example is a free-cutting machine which drives a tool 6, not shown in detail, via a drive shaft 5 mounted in a guide tube 4. The drive shaft 5 of the tool 6 is drivingly connected to a crankshaft 8 of the internal combustion engine 3 via a centrifugal clutch (Fliehkraftkupplung) 7. The crankshaft 8 rotates about a rotation axis 9 at a rotational speed n. The rotational speed n corresponds to the rotational speed of the internal combustion engine 3. The internal combustion engine 3 is advantageously started by a pull-cord starter (Seilzugstarter) 19, by a spring starter or by an electric starter motor.

Other hand-held, in particular portable, hand-held work implements can be motor chain saws, hedge trimmers (heckenschen), pole trimmers (Hochentaster), hair dryers, drills, sprinklers (Sprühgeräte) or the like.

If the rotational speed n of the internal combustion engine 3 exceeds the engagement rotational speed (Einkuppeldrehzahl) EKD (fig. 2), the centrifugal clutch 7 establishes a torque-transmitting connection between the crankshaft 8 and the drive shaft 5 of the tool 6 and drives the tool 6.

The internal combustion engine 3 has a control unit 10 for controlling a rotational speed n of the internal combustion engine 3, wherein the control unit 10 controls an ignition mechanism 11 of the internal combustion engine 3 for setting the rotational speed n. The ignition mechanism 11 is changed in accordance with the rotation speed n of the internal combustion engine 3. If the speed n exceeds a predefined upper intervention speed 49 (fig. 2), the control unit 10 intervenes in the ignition device 11 in such a way that the speed decreases. If the speed n drops below the lower intervening speed 47 (fig. 2), the ignition 11 is intervened in such a way that the speed n rises again.

A start rotational speed limiting mechanism (startrehzahlbegrenzung) 12 is configured in the control unit 10. The start-up rotation speed limiting mechanism 12 may also be provided as a separate unit. The start-up speed limiting means 12 intervenes in the ignition means as a function of the activation speed ADZ. The start-up rotational speed limiting mechanism is in standby when the internal combustion engine is started, but the pre-ignition mechanism 11 is not dried until the rotational speed n of the internal combustion engine 3 exceeds the activation rotational speed ADZ. If the speed n of the internal combustion engine 3 once (einmal) exceeds the activation speed ADZ, the start speed limiting means 12 is active. The starting rotating speed limiting mechanism intervenes in the ignition mechanism. In the active start-up speed limiting means 12, the speed n of the internal combustion engine 3 is controlled according to the predefined criteria of the method according to the invention, which is explained in more detail below.

In the method according to the invention, the start-up speed limiting means 12 intervenes in the ignition means 11 when the speed n of the internal combustion engine 3 exceeds the activation speed ADZ which lies above the engagement speed EKD. After activation, the start-up speed limiting means 12 intervenes in the ignition means 11 of the internal combustion engine 3 for at least one operating cycle asp (arbeitsspiel) of the internal combustion engine 3 in such a way that the speed n of the internal combustion engine 3 is reduced. If the speed n of the internal combustion engine 3 falls below the lower intervention speed 47, the ignition device 11 is intervened in such a way that the speed n rises again. If the speed n of the internal combustion engine 3 exceeds the upper intervention speed 49, the ignition device 11 is again intervened to reduce the speed n in such a way that the speed n is again reduced. As the number of successive duty cycles ASP increases, the upper intervention speed 49 and/or the lower intervention speed 47 changes (fig. 2).

The method according to the invention is explained below with the aid of a clock output rotational speed ATD and a clock input rotational speed ETD, which are in particular designed as characteristic curves. The characteristic curve can be a stored characteristic curve or a characteristic curve field or also be shown by an algorithm. The clock output speed ATD forms the upper intervention speed. The clock input speed forms a dry pre-rotation speed.

In the diagram according to fig. 2, the speed n (in l/min) of the internal combustion engine 3 is shown on the Y-axis. On the X-axis the number of successive working cycles ASP after Start-up (Start) and Start-up (antilaufen) of the internal combustion engine 3 is shown. One working cycle ASP in a two-stroke motor corresponds to one crankshaft revolution, i.e. 360 kW. In a four-stroke motor one working cycle ASP corresponds to two crankshaft revolutions, i.e. 720 kW.

If the internal combustion engine 3 is started at start-up, in particular by a manual pull-cord starter 19, the speed n can rise sharply in the first operating cycle ASP and exceed the activation speed ADZ. If the speed n of the internal combustion engine 3 exceeds the activation speed ADZ, the start-up speed limiting means 12 becomes active (aktiv) and intervenes in the ignition means in order to reduce the speed.

The activation rotational speed ADZ is shown in fig. 2 and is above the engagement rotational speed EKD.

Fig. 2 also shows the clock output speed ATD as a characteristic curve 14 for a continuous operating cycle ASP. The clock input speed ETD is shown as a characteristic curve 16 for a continuous operating cycle ASP. As shown in fig. 2, the

characteristic curves

14 and 16 of the clock output rotational speed ATD and the clock input rotational speed ETD decrease after the internal combustion engine 3 is started. The

characteristic curves

14 and 16 of the clock output rotational speed ATD and of the clock input rotational speed ETD change and decrease with successive operating cycles ASP. The characteristic curve advantageously drops by about (etwa) the same value. The characteristic curve 15 of the activation speed ADZ plotted against the working cycle ASP can advantageously remain unchanged against the working cycle ASP. The activation speed ADZ is also advantageously changed, in particular decreased, with respect to the working cycle ASP.

If the speed n of the internal combustion engine 3 exceeds the activation speed ADZ in the first operating cycle ASP, the start-up speed limiting means 12 is activated on the one hand, and the ignition means 11 for at least one operating cycle ASP of the internal combustion engine 3 is changed on the other hand. In a preferred embodiment of the method according to the invention, the ignition mechanism 11 is switched off. When the speed n of the internal combustion engine 3 falls below the characteristic curve 16 of the clock input speed ETD, the ignition mechanism 11 is changed, preferably switched on, again.

The characteristic curve 14 of the clock output rotational speed ATD and the characteristic curve 16 of the clock input rotational speed ETD are at a distance from one another by the rotational speed interval 13. As the number of operating cycles ASP increases, the characteristic curve 14 of the clock output rotational speed ATD and the characteristic curve 16 of the clock input rotational speed ETD decrease. After a predetermined number of successive operating cycles, the

characteristic curves

14, 16 advantageously run parallel to one another, at least over a characteristic curve section. A rotational speed channel (drehzahlkorror) 17 extending over the working cycle is advantageously formed between the

characteristic curves

14, 16. The

characteristic curves

14 and 16 define the speed channel 17. The speed channel 17 advantageously narrows as the number of successive operating cycles ASP increases. The rotational speed interval is halved over the first operating cycle. For example, the rotational speed values mentioned are illustrated.

The procedure of the method according to the invention is illustrated in the schematic flow chart of fig. 3, when the internal combustion engine is started in a start range (Startfeld) 20, it is indicated as in range 21 that the starting speed limiting means 12 is in the "stand-by mode", in the following range, a counter I is initialized, whereby a first time window 40 with a duration T1 is started, said time window 40 is started with the start of the internal combustion engine 3, with the initialization, the counter I is set to "zero", the current counter state of the counter I (Zählenstand) is queried in a decision diamond 23, the duration T1 of the time window 40 is determined by a predetermined target value of the counter I, if the duration T1 of the time window 40 has not yet ended, the counter I has not yet reached its target value, decision diamond 23 branches to the negative branch, and the counter state of the counter I has increased by a value "1" (range 24), the counter state is increased by an increment, after which, in decision 25, if the rotation speed pedal is activated, the situation is such a normal operation of the counter I, the counter I is increased by a predetermined number of the timer output of the timer branch, which is increased by a predetermined number of the timer T26, if the timer T3 is reached in a decision diamond 8, which the engine is a normal operating branch, which the timer branch is set in a decision diamond 8, if the engine speed is reached a decision diamond 8, which is a decision diamond 8, which the timer is set in a decision diamond 8, if the engine speed is reached, the engine speed is a normal operating time interval, which is reached, which is a decision diamond 8, which is set in which is reached, a decision diamond 8 is reached, a decision diamond 8 is reached, a decision d, a decision diamond 8 is.

This sequence of the method after the start of the internal combustion engine is also reproduced in fig. 4. The counter I, whose predefined target value determines the time window 40 of the duration T1, can be operated without interference, since the rotational speed n lies in the region of the rotational speed channel 17 between the clock output rotational speed ATD and the clock input rotational speed ETD according to the plotted rotational speed curve 41.

If, for example, during the duration T1 of the time window 40, it is ascertained in the decision diamond 25 (fig. 3) that the activation speed ADZ is exceeded, the decision diamond 25 branches to a further counter II. The duration T2 of the second time window 42 (fig. 5, 6) is determined for a target value predefined by the counter II. The counter II in the area 29 is initialized when the activation speed ADZ is exceeded. With initialization, the counter state is set to "zero". The counter state of counter II is queried in decision diamond 30. If the duration T2 of the time window 42 ends, the counter II has already reached its predefined target value. If the counter state of counter II has reached the target value, decision diamond 30 branches yes to zone 18 "motor off". If this is the case, the internal combustion engine 3 is switched off. There are undesirable functions which may interfere with the proper operation of the internal combustion engine 3.

The reaching of the predefined target value in the counter II is illustrated in the diagram according to fig. 5. The predefined target value of the counter II corresponds to the duration T2 of the second time window 42. During the entire time duration T2, the speed curve 43 may oscillate between the clock output speed ATD and the clock input speed ETD, which indicates an undesirable operating situation. In this case, the clock output rotational speed ADZ is exceeded and the ignition 11 is switched off, and after the rotational speed has dropped below the clock input rotational speed ETD, the ignition 11 is switched on again.

If the counter state in the counter II has not yet reached its target value, the counter state of the counter II is increased by one increment in the region 31 (fig. 3) by the decision diamond 30. Decision diamond 32 then queries whether a switch-off of ignition 11 is output, i.e. an intervention in the ignition, for example by a clock output of ignition 11. If the ignition 11 is switched off, the yes branch 33 of the decision diamond 32 returns to the decision diamond 30 in order to re-interrogate the counter state of the counter II. Furthermore, a region 39 is in the yes branch 33 leading to the decision diamond 30, in which region a further counter III is initialized.

As soon as the intervening ignition 11 is advantageously switched off, as the ignition is clocked out, for example, decision diamond 32 branches back to decision diamond 30 via yes branch 33 until the target value of counter II is reached. Decision diamond 30 then branches to zone motor stop 18. The combustion engine 3 is switched off accordingly. With the yes branch through decision diamond 32-each time the counter state of counter II is queried back in decision diamond 30, counter III is set to "zero". A target value is predefined for the counter III, which target value corresponds to the duration T3 (fig. 4, 5) of the third time window 44.

If the ignition is not clocked out, advantageously switched off, in the duty cycle ASP, decision diamond 32 branches via no-branch 34 to area 35 where the counter state of counter III is increased by one increment. It is then queried by decision diamond 36 whether the counter state of counter III has reached the set target value. The target value of the counter III corresponds to the duration T3 of the third time window 44. If duration T3 ends, which is recognized by reaching the target value for the counter state of counter III, decision diamond 32 branches to region 38 via the yes-branch. The region 37 allows the speed n of the internal combustion engine 3 to increase beyond the clock output speed (upper intervention speed), so that the internal combustion engine 3 is in normal operation.

Alternatively, it can be checked in the region 38 whether a shut-off criterion for shutting off (Abschalten) the starting speed limiting means 12 is present and whether a switchover to normal operation of the internal combustion engine 3 is possible. The shut-down criterion can be an operating variable signal of the internal combustion engine or an ignition control of the internal combustion engine, as described, for example, in patent application DE 102011010069 a1 of the present applicant. If the switch-off criterion is present, a return is made to an operating mode of the internal combustion engine 3 in order to operate as the work apparatus 1.

Conversely, if the duration T3 of the third time window 44 has not ended, i.e., the target value of counter III has not been reached in the illustrated embodiment, decision diamond 36 branches to the no-branch and back to the beginning of decision diamond 30. In decision diamond 30, it is again queried whether the target value of counter II has been reached, i.e. whether the duration T2 of the second time window 42 has ended.

The counter III forms a third time window 44 of duration T3 and is reinitialized when the ignition 11 is switched off. This is illustrated in fig. 3, in which decision diamond 32 branches off via yes branch 33 into region 39. In this branch 33, the counter state of the counter III is reset to "zero" respectively.

As can also be seen from fig. 5, with the activation speed ADZ being exceeded, a second time window 42 of duration T2 is initiated and a third time window 44 of duration T3 is initiated via a speed curve 43 after the ignition 11 has been switched on and below the clock input speed ETD. If the speed curve 43 exceeds the clock output speed ATD after activation of the second time window 42, the ignition 11 is switched off. As can be seen from the schematic flow chart according to fig. 3, in this case decision diamond 32 branches back to the beginning of decision diamond 30 via yes branch 33, wherein at the same time the counter state of counter III is erased or counter III is reinitialized. The counter III counts up again from "zero" provided that the ignition 11 is switched on again. The third time window 44 resumes operation for a duration T3.

If, as shown in fig. 6, during the duration T2 of the second time window 42, the speed curve 45 is below the clock output speed ATD, the duration T4 of the third time window 44 may end undisturbed, so that, as shown in fig. 3, the decision diamond 36 branches to the region 38. With reaching the region 38, the internal combustion engine 3 is switched into normal operation for operation as the industrial appliance 1.

A comparison of fig. 5 and 6 shows that after the activation speed ADZ has been exceeded, a second time window 42 of duration T2 is initiated. If the speed n of the internal combustion engine is not below the clocked output speed ATD for the duration T3 of the third time window 44, then the internal combustion engine 3 is advantageously switched off. In the diagram of fig. 5, the rotational speed curve 43 exceeds the clock output rotational speed ATD after the ignition 11 has been switched on, so that the third time window 44 cannot be ended. In fig. 6, the speed curve 45 is pivoted below the clocked output speed ATD, so that the duration T3 of the third time window 44 can end, which means a stable operation of the internal combustion engine 3.

As can be further seen from fig. 4 to 6, the duration T2 of the second time window 42 is longer than the duration T1 of the first time window 40 and/or the duration T3 of the third time window 44. The duration of the second time window 42 is many times longer than the duration T3 of the third time window. The duration T2 of the second time window is three to ten times as long, in particular eight times as long, as the duration T3 of the third time window 44.

As can also be seen from fig. 4 to 6, the duration T1 of the first time window 40 is longer than the duration T3 of the third time window 44. In the illustrated embodiment, the duration T1 of the first time window 40 is two to four times as long as the duration T3 of the third time window 44. In particular, the duration T1 of the first time window 40 is twice as long as the duration T3 of the third time window 44.

The target values of the counters I, II and III are predefined as a function of the selected duration T1 of the first time window 40, the duration T2 of the second time window 42 and the duration T3 of the third time window 44. The target value of the second counter II is therefore larger than the target value of the first counter I and/or the target value of the third counter III. The target value of the second counter II is in particular a multiple of the target value of the third counter III.

The first time window 40 may also be referred to as a start window. The second time window 42 may also be referred to as a control window. The third time window 44 may also be referred to as a monitoring window.

Claims

1. Method for starting an internal combustion engine (3) in a handheld portable work apparatus (1), wherein a tool (6) of the work apparatus (1) is drivingly connected to a crankshaft (8) of the internal combustion engine (3) by means of a centrifugal force clutch (7), and wherein the centrifugal force clutch (7) drives the tool (6) when a rotational speed (n) of the internal combustion engine (3) exceeds an engagement rotational speed (EKD) of the centrifugal force clutch (7), and wherein a control unit (10) is provided for controlling the rotational speed (n) of the internal combustion engine (3), wherein the control unit (10) controls an ignition mechanism (11) of the internal combustion engine (3) for adjusting the rotational speed (n) and changes the ignition mechanism (11) as a function of the rotational speed (n) of the internal combustion engine (3),

it is characterized in that the preparation method is characterized in that,

(i) a start rotational speed limiting device (12) is provided, which intervenes in the ignition device (11) when the rotational speed (n) of the internal combustion engine (3) exceeds an activation rotational speed (ADZ) above an engagement rotational speed (EKD),

(ii) the start-up speed limiting means (12) intervenes in the ignition means (11) of the internal combustion engine (3) during at least one operating cycle (ASP) of the internal combustion engine (3) in such a way that the speed (n) of the internal combustion engine (3) is reduced,

(iii) and after the rotational speed (n) of the internal combustion engine (3) has dropped below a lower intervention rotational speed (47) below an upper intervention rotational speed (49) in a rotational speed interval (13), the ignition device (11) is intervened in such a way that the rotational speed (n) increases,

(iv) and, if the rotational speed (n) of the internal combustion engine (3) exceeds the upper intervention rotational speed (49), the ignition device (11) is intervened in such a way that the rotational speed (n) drops again,

(v) and the upper intervention speed (49) and/or the lower intervention speed (47) is/are changed as the number of successive work cycles (ASP) increases.

2. Method according to claim 1, characterized in that the upper intervention speed (49) and/or the lower intervention speed (47) is/are reduced.

3. Method according to claim 1, characterized in that the upper intervention speed (49) is a clock output speed (ATD), and the ignition (11) is switched off when the upper intervention speed is exceeded.

4. Method according to claim 1, characterized in that the lower intervention speed (47) is a clock input speed (ETD), below which the ignition (11) is switched on.

5. Method according to claim 1, characterized in that the upper intervention speed (49) is plotted as a characteristic curve (14) for a continuous operating cycle (ASP) and the lower intervention speed (47) is plotted as a characteristic curve (16) for a continuous operating cycle (ASP).

6. Method according to claim 5, characterized in that the characteristic curves (14, 16) of the upper intervention speed (49) and of the lower intervention speed (47) are extended at least partially parallel to each other for successive operating cycles (ASP) after the starting of the internal combustion engine (3).

7. Method according to claim 5, characterized in that the characteristic curve (14, 16) of the upper intervention speed (49) and/or of the lower intervention speed (47) is changed with a continuous work cycle (ASP).

8. Method according to claim 7, characterized in that the characteristic curves (14, 16) of the upper intervention speed (49) and of the lower intervention speed (47) are reduced by the same amount.

9. Method according to claim 7, characterized in that the characteristic curves (14, 16) of the upper intervention speed (49) and of the lower intervention speed (47) are reduced by different values.

10. Method according to claim 1, characterized in that said activation speed (ADZ) is greater than or equal to said upper intervention speed (49).

11. Method according to claim 1, characterized in that, when the speed (n) of the internal combustion engine (3) is below the upper intervention speed (49) during the entire duration (T1) of the first time window (40), the upper intervention speed (49) is allowed to be exceeded after the start of the internal combustion engine (3) after the end of the first time window (40).

12. Method according to claim 11, characterized in that a second time window (42) is started with the activation speed (49) being exceeded and the internal combustion engine (3) is switched off when the speed (n) of the internal combustion engine (3) is not below the upper intervention speed (49) for the duration (T3) of a third time window (44).

13. Method according to claim 12, characterized in that the duration (T2) of the second time window (42) is longer than the duration (T1) of the first time window (40) and/or the duration (T3) of the third time window (44).

14. The method according to claim 12, characterized in that the duration (T2) of the second time window (40) is at least a multiple longer than the duration (T3) of the third time window (44).

15. The method according to claim 12, characterized in that the duration (T1) of the first time window (40) is longer than the duration (T3) of the third time window (44).

16. Method according to claim 12, characterized in that in the operation of the start speed limiting means (12), the third time window (44) is restarted with each undershooting of the lower intervention speed (47) and the intervention of the ignition means (11).

17. Method according to claim 12, characterized in that said upper intervention speed (49) is allowed to be exceeded when there is no intervention of the ignition mechanism to reduce the speed during the duration (T3) of said third time window (44).

18. Method according to claim 1, characterized in that the internal combustion engine (3) is started by means of a pull-cord starter (19).